Oil diffusion pump with cooled baffle



Dec. 26, 1967 R. STUFFER 3,360,188

OIL DIFFUSION PUMP WITH COOLED BAFFLE 2 Sheets-Sheet 1 Filed Feb. 2, 1966 //VVE/VT0/?.

STUFFER 96 ROWEN ATTORNEYS.

Dec. 26, 1967 R. STUFFER 3,360,188

OIL DIFFUSION PUMP WITH COOLED BAFFLE Filed Feb. 2, 1966 2 Sheet t 2 WVE/VTOR, ROWEN sT A NEY United States Patent 3,360,188 OIL DIFFUSION PUMP WITH COOLED BAFFLE Rowen Staffer, 20 Glenview Lane, Willingboro, NJ. 08046 Filed Feb. 2, 1966, Ser. No. 524,513 Claims. (Cl. 230-101) ABSTRACT OF THE DISCLOSURE An oil diffusion pump having adjacent its upper inlet at least three inclined internal planar overlapping coudensing baflie's intersecting at the center of the pump to condense upwardly moving internal oil vapor but permit Without substantial hindrance the downward flow of gases through the baffles and into the pump.

This invention pertains to an oil diffusion pump having a cooled bafiie and more particularly to a novel oil diffusion pump which achieves results heretofore unobtainable, except with the inclusion of special equipment externally of the pump.

The use of an oil diffusion pump in industry is now well established for the purpose of securing a very high vacuum. The oil diffusion pumps now in use generally involve the evaporation of oil as a pumping fluid in a closed container by a boiler with the resulting oil vapor being directed in a stream at a high velocity through a nozzle system against the internal wall of a container or pump body. The high speed oil vapor stream traps by diffusion gas molecules from the area being evacuated and compresses such molecules into a higher pressure area that is in communication with a mechanical backing pump. The high velocity vapor stream is intended to be condensed by contact with the walls of the container which may be positively cooled through the use of an outer water jacket. The condensed liquid returns to the broiler to be reheated, and the cycle starts again.

As a practical matter, the high velocity vapor stream is not always completely condensed, so that small amounts of the vapor eventually work their way into the area to be evacuated, thereby decreasing the high vacuum and causing possible fouling. It has been found that some of the vapor will also work its way into the mechanical pump, and thereby constitute a loss of vaporized material. This loss is objectionable because of the high expense of the vaporized material.

The working back of the vapor into the area to be evacuated is well known in the art as backstreaming. Numerous suggestions have been made in order to minimize or eliminate backstreaming.

It is known to employ a separately constituted water cooled baffle that is positioned upstream of the oil diffusion pump, between the oil diffusion pump and the area to be evacuated. In this way, any vapor escaping upstream of the oil diffusion pump is condensed by the bat-He before it reaches the area to be evacuated. However, the use of a separate baflle entails extra expense and is objectionable in that the air flow or conductance is severely limited, and this seriously lessens the capacity of the oil diffusion pump and necessitates the use of a larger diffusion pump to maintain the required pumping speed.

Another suggestion is the use of a cold cap which is positioned on at least one of the vapor jet nozzles. However, the use of cold caps is objectionable from the standpoint of added expense, as well as the fact that the cold cap is ineffective as to the peripheral internal areas of the oil diffusion pump, and thus backstreaming occurs anyway.

It is therefore an object of the present invention to "ice provide an oil diffusion pump with cooled baffle that substantially eliminates backstreaming but does not adversely affect conductance or air flow.

Yet another object of the present invention is to provide an oil diffusion pump with an internal cooled bafile which does not entail the use of a costly separately disposed upstream bafile, but instead is a part of the oil diffusion pump itself at little added cost.

Yet another object of the present invention is to provide an oil diffusion pump having an outer water jacket in thermal communication with an internal baffie system.

Still another object of the present invention is to provide an oil diffusion pump with bafi'le having an external water jacket with corrugations being provided in the water jacket in order to achieve a uniformity of water temperature.

Yet another object of the present invention is to pro vide an oil diffusion pump with baffle including a lower cooling chamber to effect a quick cooling of the relatively expensive oil upon cessation of the operation of the oil diffusion pump, and thereby protect the oil from air oxidation at elevated temperature.

The foregoing as well as other objects of the invention are achieved by providing an oil diffusion pump which is basically comprised of conventional elements, such as a container or cylindrical pump body housing a vapor jet assembly with the inclusion of a boiler for purposes of vaporizing the oil. The cylindrical pump body has an outer water cooling jacket which is defined in part by a corrugated wall for purposes of achieving temperature uniformity. The oil diffusion pump also includes a conventional foreline which is also water cooled in part to assure complete coverage of the inlet opening, but in such a manner that air flow is not substantially impeded. The cooling effect of the water jacket is conveyed directly to the bafiles because of their connection to the cylindrical pump body.

The bafiles of the present invention are considered to be condensing means in good thermal communication with positive cooling means. The condensing means of the present invention extend into the vacuum air stream across substantially the entire flow area of the upper inlet opening with the possible exception of a small cen tral circular area spaced above the topmost vapor cap for increasing air flow or conductance.

The inclined angle of the baffles is such that air flow or conductance is not substantially hindered. The baflies preferably extend to a point below the topmost vapor jet cap in order to exert a maximum condensing action upon the oil vapor at points closest to the cylindrical pump body where the prior art devices were most ineffective.

Other objects and many of the attendant advantages of this invention will be readily appreciated as the same becomes better understood by reference to the following detailed description when considered in connection with the accompanying drawings wherein:

FIG. 1 is a side elevational view of a baflled oil diffu-,

sion pump constituting an embodiment of the present invention;

FIG. 2 is a somewhat enlarged top plan view taken FIG. 4 is a sectional view taken along the lines 4--4 of FIG. 3;

FIG. 5 is a sectional view taken along the lines 5-5 of FIG. 3;

FIG. 6 is an enlarged sectional view taken along the lines 6-6 of FIG. 5;

FIG. 7 is a sectional view taken along the lines 77 of FIG. 3;

FIG. 8 is an enlarged sectional view taken along the lines 8-8 of FIG. '7;

FIG. 9 is an enlarged perspective view illustrating three battles secured together in accordance with the present invention; and

FIG. 10 is a top plan view similar to FIG. 2 wherein there is a circular central open area provided for in the bat-lies for flow increasing.

Referring now in greater detail to the various figures of the drawing wherein like reference characters refer to like parts there is shown at 10 in FIG. 1 an oil diffusion pump constituting a first embodiment of the present invention.

The pump 10 basically comprises a cylindrical pump body 12 having a vapor jet assembly 14 contained therein as shown in FIG. 3. The pump body 12 also includes adjacent the bottom thereof heating means or boiler 16. The oil diffusion pump 10 communicates with the area to be evacuated (not shown) through upper inlet 18, and a mechanical pump (not shown) communicates with the oil diffusion pump foreline 20.

As also shown in FIG. 3 baflles 22, 24 and 26 are positive condensing means that are secured to the sides of the pump body 12 adjacent upper inlet 18 for the purpose of substantially eliminating backstreaming as will be discussed in greater detail hereinafter. Finally the diffusion pump 10 includes an external water jacket 28 in thermal communication with the positive condensing means, and fitted about the external surface of the pump body 12.

The vapor jet assembly 14 includes a plurality of nozzles 30, 32 and 34 that will direct oil vapor in a stream at a high velocity against the internal wall of pump body 12. The details of the vapor jet assembly 14 and the nozzles 30, 32 and 34 as well as the oil vapor circulating system are well known in the art. The oil lays in a puddle at the bottom of the pump body 12 adjacent heating means 16 until vaporized by the heating means 16, at which time the oil vapor will rise through the vapor jet assembly 14. Some of the oil vapor is discharged in a high velocity vapor stream through openings 36 in the lowermost nozzle 30. However, a considerable amount of the oil vapor will pass upwardly through the riser 38 to be discharged through openings 40 in the intermediate nozzle 32. Yet additional oil vapor will pass upwardly through the riser 42 to be discharged through openings 44 in top nozzle 34.

The oil vapor as discharged from any of the nozzles 30, 32 and 34 is directed in a high velocity stream downwardly against the internal wall of the pump body 12 by virtue of the shielding effect of the cap that is spaced immediately from openings 36, 40 and 44. The topmost cap may be shielded by a separate radiation shield.

The heating means 16 may consist of an elongated strip of electrically conductive material of somewhat high resistance, wound into many turns in toroid form as generally shown at 46 in FIG. 3. The liquid oil is intended to lay in a puddle in oil space 48 that communicates with vapor space 50. In this manner a level of liquid oil is constantly fed from oil space 48 to vapor space 50 so that the heat from boiler 16 may be used to create oil vapor that will then pass upwardly into nozzle 30 in a manner well known in the art.

Further details of the heating means 16 are shown in FIGS. 4 and 5 as including insulating spacer members 52 and appropriately insulated electrical terminals 54 with lower insulator bushings 56. A support plate 58 (FIG. 5) also includes grooves 60 for better heat con- 4. duction in connection with the quick oil cooling feature of the invention to be described hereinafter.

As also shown in FIG. 4 there is a lower flange 62 with bolts 64 with the base 58 being secured to a lower plate 66 by bolts 68. The heating means 16 is appropriately electrically insulated from the other metallic parts of the oil diffusion pump in a manner well known to those skilled in the art.

The annular water jacket 28 is comprised of an outer shell 70 with downwardly inclined spiral corrugations 72 (FIGS. 1 and 3) which achieve temperature uniformity in the water jacket by creating eddy currents or flow currents as the cooling water circulates through the water jacket 28. The outer shell 70 is simply welded or otherwise secured to the outer wall of the pump body 12. This is superior to the use of conventional copper tubing that is usually soldered to the pump body. With copper tubing hot spots could develop between the coils. Also, if Water flow is interrupted, the heat emanating from the pump heater will melt the solder connector of the copper tubing. Furthermore, the copper tubing is easily dented, thereby restricting water flow.

The water is fed through upper inlet 74 (FIG. 2) and then passes downwardly through the water jacket 28 and then upwardly through tubing 76 (FIG. 1) to the foreline water jacket 78 to be discharged through outlet 80. The direction of water travel may be reversed if so desired. As best shown in FIG. 2 the upper inlet 18 includes a flange 82 with openings 84, and the foreline 20 has a flange 86 with openings 88 for fastening purposes.

The details of the bafiles 22, 24 and 26 are best shown in FIGS. 2, 3 and 9. It is preferred that there be at least two battles and preferably three bafiles that optically close upper inlet 18. In order to do this the bafiles 22, 24 and 26 are overlapping as indicated in FIGS. 3 and 9. However, such overlapping exists in such a manner that air flow is not substantially impeded, since a particular battle closes off no more than /3 or 120 of the opening constituting upper inlet 18 as shown in FIG. 2. Thus gases may work their way around and beneath the various bafiles in order to obtain access to the lower internal portions of the pump body 12. The number and size of the baflies may vary as will be apparent to those skilled in the art.

As best shown in FIG. 3 the bafiles 22, 24 and 26 have their outer edges brazed, welded, soldered or otherwise secured by a conductive material to the inner wall of the pump body 12. It is important that the pump body 12 as well as the baffles be formed from a heat conductive material, such as aluminum or stainless steel, so that the cooling effect of the water in the jacket 28 may be efficiently transferred through the wall of the pump body 12 to the bafiles 22, 24 and 26. In other words, the heat conductive circuit extending between the water jacket 28 and the baflles may be likened to an electrical circuit of low electrical resistance.

The baifies of the present invention are shown to be planar although they may be appropriately curved to enhance the air flow or to present less resistance to the air flow, and still fall within the purview of the present invention. The battles of the present invention may be referred to as positive overlapping condensing means since they are in good thermal communication with the water jacket 28 that constitutes positive cooling means.

The baffles or positive condensing means of the present invention extend either entirely across substantially the entire flow area of upper inlet 18, or cover the entire area with the exception of a small central circular opening 90 as shown in FIG. 10. The opening 90 should be no larger than the circular area 92 (FIG. 3) of the topmost cap that shields openings 44 of topmost nozzle 34 for increasing air flow or conductance.

The 'bafiles 22, 24 and 26 may be additionally supported by a central stud 94 (FIG. 9) which may rest on or be supported by a jet cap. The stud 94 can have inclined slots which accept a small portion of the inner edge of each of the batfies at spaced portions along the length of the stud. Where the central opening 90 is present, the stud 94 has a much larger inner diameter which actually defines the opening 90.

As shown in FIG. 3 the overlapping bafiles 22, 24 and 26 lie at an acute angle with respect to the vertical, with each lying at a convenient angle so as not substantially to obstruct air flow. It is desirable that all of the bafiles be in actual thermal contact with the water jacket, but this will be a matter of design that will occur to those skilled in the art. It is, however, necessary to the present invention that at least one baflle be in good thermal contact with the water jacket.

The term good thermal contact as used herein and in the claims is to be understood to mean sufi'icient proximity of the cooling effect of the water jacket that such cooling effect is readily or efliciently transmitted. In order to achieve good thermal contact, it is preferred that there be a direct conductive connection between the bafiie and the water jacket, such as through a highly conductive material as would be used in Welding or brazing, with the pump body 12 also being made of a highly thermal conductive material.

It is thus seen that the cooling action of the water jacket is quickly and directly conveyed through the wall of the pump body 12 to the baffles which are in good thermal contact therewith, and thence across the battles of the central area. While certain of the prior art devices did use a cooling coil, it was the area located lying away from the internal wall of the pump body which allowed backstreaming to persist. This area was spaced far enough away from the wall of the pump body that it was beyond the thermal reach of the water jacket. Where it was attempted in the prior devices to provide internal cooling devices, such as the cold cap, such devices were inadequate because they were confined to the central portions of the pump body and neglected that portion of the flow area between the central portion spaced from the wall. It is seen that the present invention provides an excellent cooling effect in the aforesaid region without substantially interrupting gaseous flow. It is further preferred that the baffies 22, 24 and 26 extend to a point below the topmost vapor jet cap as shown in FIG. 3 in order to prevent a longer cooling area that will be most efiicient in condensing the oil vapor.

It is thus seen that the present invention provides an elfective solution to the problem of backstreaming by exerting a positive condensing efiect upon the oil Vapor across substantially the entire fiow area.

Because of the great expense of the oil used in oil diitusion pumps, it is important to protect the oil from oxidation at high temperatures that is likely to occur after the action of the pump has been stopped and sufficient time has passed to break the vacuum. Under such circumstances, it has been found that the expensive oil will tend to oxidize because it is still very hot. This problem is solved in the present invention by providing a lower cooling chamber 96 (FIG. 3) that is effective against a lower plate 98 (FIGS. 3, 7 and 8) with grooves 60 for providing a greater surface area for cooling purposes. This allows cooling water to penetrate into area 100 (FIG. 8) which is sealed by rings 102 and 104. The lower cooling chamber 96 is, of course, operative only upon shutdown of the oil diffusion pump, and will quickly cool the oil deposited in a puddle in the areas 48 and 50. For similar reasons of economy, the foreline water jacket 78 is provided to be effective during the operation of the oil diffusion pump to condense any oil vapor that might escape through the foreline into the mechanical pump.

Obviously, many modifications and variations of the present invention are possible in the light of the above teachings. It is, therefore, to be understood that within 6.1 the scope of the appended claims, the invention may be practiced otherwise than as specifically described.

What is claimed as the invention is:

1. In an oil diffusion pump utilizing oil and including a pump body having a vacuum inlet and a discharge foreline comprised of a wall of a material of good thermal conductivity, said pump body housing a boiler and a vapor jet assembly to convert said oilto oil vapor, said boiler vaporizing oil through said vapor jet assembly and toward said pump body, the improvement comprising providing cooling means in gool thermal communication with said wall and positive overlapping condensing means in said pump body extending above said vapor jet assembly to prevent oil backstreaming, said condensing means including at least three inclined planar overlapping heat conductive baflles each having edges in actual good thermal contact with said wall and said cooling means in order to convey the effect of said cooling means through said bafiles, said overlapping baifies intersecting at the center of said pump body and extending across said upper inlet to collectively close off substantially said entire upper inlet to prevent direct upward escape of said oil vapor and also to exert a condensing action across said upper inlet, but said batfies being at least in part spaced from one another to permit without substantial hindrance the flow of gases through said upper inlet and downwardly through said pump body while blocking upward backstreaming of said oil vapor and exerting the condensing action on said oil vapor across substantially said entire upper inlet.

2. The invention of claim 1 wherein said positive cooling means is an external water jacket defined by an outer shell secured to a portion of said external surface, and having water inlet and discharge openings.

3. The invention of claim 2 wherein corrugations are provided in said wall and said shell.

4. The invention of claim 2 wherein positive cooling means are associated with at least a portion of said foreline.

5. The invention of claim 1 wherein said baflles are secured along a portion of their edges to said internal surface by brazing using a good thermally conductive material.

6. The invention of claim 1 wherein said vapor jet assembly is comprised of a topmost nozzle that is shelded by a cap and a radiation shield, said upper inlet being completely optically closed with the exception of a small central area no larger than the dimensions of said shield and spaced above said cap.

7. The invention of claim 6 wherein said battles are disposed at angles with respect to each other, with said bafiles extending away from said upper inlet and free edges thereof extending below said shield.

8. The invention of claim 1 including a lower cooling chamber that is operative uponshutdown for purposes of quickly cooling the oil to prevent oxidation thereof.

9. The invention of claim 1 wherein said cooling means is an external water jacket having corrugations in contact with said pump body and having water inlet and discharge openings.

10. The invention of claim 9 wherein said corrugations are in the form of a downwardly extending spiral with the water being led in ribbons between said corrugations downwardly through said water jacket thereby avoiding channelling of water.

References Cited UNITED STATES PATENTS 2,078,788 4/1937 Bancroft 230-10l 2,249,450 7/ 1941 Bancroft 230101 2,291,054 7/1942 Nelson 230l0l (Other references on following page) UNITED STATES PATENTS OTHER REFERENCES 2 3 293 1 1945 Downing 230 101 T-M Vacuum Products, Bulletin 402, High Speed, 2,508,765 5/1950 Morand 230 101 High-Vacuum Diffusion Pumps, y 1967- 31117714 1/1964 AuPoiX 230-101 5 ROBERT A. OLEARY, Primary Examiner. 3,168,819 2/1965 Santeler 230-101 3 203 24 19 5 smith 230 101 DONLEY J. STOCKING, ROBERT M. WALKER, 3,258,196 6/1966 Knox et a1. 230101 Examiners.

3,288,354 11/1966 Dennis 230-101 W. J. KRAUSS, Assistant Examiner. 

1. IN AN OIL DIFFUSION PUMP UTILIZING OIL AND INCLUDING A PUMP BODY HAVING A VACUUM INLET AND A DISCHARGE FORELINE COMPRISED OF A WALL OF A MATERIAL OF GOOD THERMAL CONDUCTIVITY, SAID PUMP BODY HOUSING A BOILER AND A VAPOR JET ASSEMBLY TO CONVERT SAID OIL TO OIL VAPOR, SAID BOILER VAPORIZING OIL THROUGH SAID VAPOR JET ASSEMBLY AND TOWARD SAID PUMP BODY, THE IMPROVEMENT COMPRISING PROVIDING COOLING MEANS IN GOOL THERMAL COMMUNICATION WITH SAID WALL AND POSITIVE OVERLAPPING CONDENSING MEANS IN SAID PUMP BODY EXTENDING ABOVE SAID VAPOR JET ASSEMBLY TO PREVENT OIL BACKSTREAMING, SAID CONDENSING MEANS INCLUDING AT LEAST THREE INCLINED PLANAR OVERLAPPING HEAT CONDUCTIVE BAFFLES EACH HAVING EDGES IN ACTUAL GOOD THERMAL CONTACT WITH SAID WALL AND SAID COOLING MEANS IN ORDER TO CONVEY THE EFFECT OF SID COOLING MEANS THROUGH SAID BAFFLES, SAID OVERLAPPING BAFFLES INTERSECTING AT THE CENTER OF SAD PUMP BODY AND EXTENDING ACROSS SAID UPPER INLET TO COLLECTIVELY CLOSE OFF SUBSTANTIALLY SAID ENTIRE UPPER INLET TO PREVENT DIRECT UPWARD ESCAPE OF SAID OIL VAPOR INLET, BUT SAID BAFFLES BEING AT LEAST IN ACROSS SAID UPPER INLET, BUT SAID BAFFLES BEING AT LEAST IN PART SPACED FROM ONE ANOTHER TO PERMIT WITHOUT SUBSTANTIALLY HINDRANCE THE FLOW OF GASES THROUGH SAID UPPER INLET AND DOWNWARDLY THROUGH SAID PUMP BODY WHILE BLOCKING UPWARD BACKSTREAMING OF SAID OIL VAPOR AND EXERTING THE CONDENSING ACTION ON SAID OIL VAPOR ACROSS SUBSTANTIALLY SAID ENTIRE UPPER INLET. 